The present invention is related to current controlled drivers, and more particularly to a current controlled driver having a low voltage control circuit directly coupled to a high voltage capable controlled AC driver circuit.
There are a number of methods and techniques that have been developed for controlling the current through loads such as fluorescent lamps (FLs) including compact fluorescent lamps (CFLs) and cold cathode fluorescent lamps (CCFLs) that use one or more transformers for multiple lamps. Some of these methods control the current through the FL, CFL or CCFL from the primary side while others control from the secondary side. Control of the secondary side typically includes rectifying the alternating current (AC) from the transformer into a direct current (DC) using a bridge rectifier similar to a conventional AC to DC power supply (for example see U.S. Pat. No. 7,183,724, “Inverter with Two Switching Stages for Driving Lamp”, U.S. Pat. No. 6,462,485, “EL Driver for Small Semiconductor Die”, U.S. Pat. No. 6,927,989, “DC-AC Converter and Controller IC for the Same”, U.S. Pat. No. 7,298,095, “Discharge Lamp Ballast Apparatus”, and U.S. Pat. No. 6,081,075, “DC To AC Switching Circuit For Driving An Electroluminescent Lamp Exhibiting Capacitive Loading Characteristics”). Such methods and approaches require very careful balancing or blocking of the DC current such that there is no net DC current flowing through the FL, CFL or CCFL as a DC current component can greatly reduce the life of the FL, CFL or CCFL. Control of AC methods often require isolation of the control circuitry on the primary side (low) voltage potential which is referenced to ground (zero) potential from the secondary (high) side in which the electronics may be floating and not directly tied to ground potential. For example, such isolation can consist of using an opto isolator and/or opto coupler as is required in U.S. Pat. No. 7,151,345, “Method And Apparatus For Controlling Visual Enhancement Of Luminent Devices” and U.S. Pat. No. 7,151,246, “Method And Apparatus For Optimizing Power Efficiency In Light Emitting Device Arrays” in which complex digital algorithms are used and require the use of, for example, field programmable logic arrays (FPGAs) to interface to various control blocks including isolated read and sense units via opto-isolators.
Furthermore optocouplers/optoisolators are often relatively expensive for such an application as multiple CCFLs and are not amenable to incorporation and monolithic inclusion into integrated circuit (IC) approaches and need to use opto-isolation or other such non-IC integration approaches as external components to the ICs.
Thus, for at least the aforementioned reason, there exists a need in the art for improved current controlled drivers.